Induced charge transfer in ih-scn@c80 derivatives

Published on Web 05/15/2009

Photoinduced Charge Transfer and Electrochemical Properties of Triphenylamine Ih-Sc3N@C80 Donor-Acceptor Conjugates
Julio R. Pinzon,† Diana C. Gasca,† Shankara G. Sankaranarayanan,§ ´ Giovanni Bottari,‡ Tomas Torres,‡ Dirk M. Guldi,§ and Luis Echegoyen*,† ´
Department of Chemistry, Clemson UniVersity, Clemson, South Carolina 29634, Department of Chemistry andPharmacy and Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-UniVersitat Erlangen-Nurnberg, Egerlandstrasse 3, ¨ ¨ 91058 Erlangen, Germany, and Departamento de Quımica Organica, UniVersidad Autonoma de ´ ´ ´ Madrid, E-28049 Madrid, Spain
Received January 29, 2009; E-mail: luis@clemson.edu

Abstract: Two isomeric [5,6]-pyrrolidine-Ih-Sc3N@C80 electron donor-acceptorconjugates containing triphenylamine (TPA) as the donor system were synthesized. Electrochemical and photophysical studies of the novel conjugates were made and compared with those of their C60 analogues, in order to determine (i) the effect of the linkage position (N-substituted versus 2-substituted pyrrolidine) of the donor system in the formation of photoinduced charge separated states, (ii) thethermal stability toward the retro-cycloaddition reaction, and (iii) the effect of changing C60 for Ih-Sc3N@C80 as the electron acceptor. It was found that when the donor is connected to the pyrrolidine nitrogen atom, the resulting dyad produces a significantly longer lived radical pair than the corresponding 2-substituted isomer for both the C60 and Ih-Sc3N@C80 dyads. In addition to that, theN-substituted TPA-Ih-Sc3N@C80 dyad has much better thermal stability than the 2-subtituted one. Finally, the Ih-Sc3N@C80 dyads have considerably longer lived charge separated states than their C60 analogues, thus approving the advantage of using Ih-Sc3N@C80 instead of C60 as the acceptor for the construction of fullerene based donor-acceptor conjugates. These findings are important for the design andfuture application of Ih-Sc3N@C80 dyads as materials for the construction of plastic organic solar cells.

Introduction

Fullerenes have been proposed as acceptor materials in the construction of plastic solar cell devices due to their unique structural and electron acceptor characteristics.1 Most of the fullerene-based solar cells are made using the bulk heterojunction concept, where aconjugated polymer acting as a donor is blended with a fullerene derivative with improved solubility acting as the acceptor.2 The maximum power conversion efficiencies with this type of cells have recently reached 5.5%.3 Hence higher efficiencies seem to be feasible, both theoretically and in practice.4 The molecular heterojunction concept where
Clemson University. Friedrich-Alexander-UniversitätErlangen-Nürnberg. ‡ Universidad Autónoma de Madrid. (1) (a) Thompson, B. C.; Frechet, J. M. J. Angew. Chem., Int. Ed. 2008, 47, 58–77. (b) Araki, Y.; Ito, O. J. Photochem. Photobiol., C. 2008, 9, 93–110. (c) Imahori, H. Bull. Chem. Soc. Jpn. 2007, 80, 621–636. (d) Guenes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. ReV. 2007, 107, 1324–1338. (e) Blom, P. W. M.; Mihailetchi, V. D.; Koster, L. J. A.; Markov,D. E. AdV. Mater. 2007, 19, 1551–1566. (f) Koeppe, R.; Sariciftci, N. S. Photochem. Photobiol. Sci. 2006, 5, 1122–1131. (2) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science 1995, 270, 1789–1791. (3) (a) Lee, J. K.; Ma, W. L.; Brabec, C. J.; Yuen, J.; Moon, J. S.; Kim, J. Y.; Lee, K.; Bazan, G. C.; Heeger, A. J. J. Am. Chem. Soc. 2008, 130, 3619–3623. (b) Peet, J.; Kim, J. Y.;Coates, N. E.; Ma, W. L.; Moses, D.; Heeger, A. J.; Bazan, G. C. Nat. Mater. 2007, 6, 497– 500. (c) Kim, J. Y.; Lee, K.; Coates, N. E.; Moses, D.; Nguyen, T.; Dante, M.; Heeger, A. J. Science 2007, 317, 222–225.
§ †

a donor molecule is covalently connected to a fullerene is one of the possible alternatives to further improve the efficiency of plastic fullerene-based solar cells.5 Since organic...